1. Field of the Invention
The present invention concerns a method for generating T1-weighted images of an examination subject by means of magnetic resonance. The invention is particularly suitable in the use of fast spin echo imaging sequences with which a T1 contrast should be achieved. For example, the invention can be used in the acquisition of images of the brain to differentiate between white and grey brain matter. Naturally it can also be applied in other examination regions in which a T1 contrast is desirable.
2. Description of the Prior Art
Two-dimensional spin echo imaging sequences are typically used to achieve a T1 contrast in magnetic resonance images (MR images). However, these sequences have the disadvantage of a long acquisition time. This can be shortened by switching longer echo trains with a number of refocusing pulses. However, given longer echo trains with a number of refocusing pulses the problem arises that the T1 contrast is worsened since the detected signals receive an increased T2 weighting in the course of the echo train.
Furthermore, three-dimensional spin echo imaging methods have been developed in which refocusing pulses with different flip angles have been used after a spatially non-selective excitation pulse, making the use of longer echo trains was possible (see Mugler J P et al. in “Three-dimensional spin-echo-train proton-density-weighted imaging using shaped signal evolutions”; 1999 in Proceedings of the 7th Annual Meeting of ISMRM, Philadelphia, USA, page 1631 and Mugler et al. in “Optimized single-slab three-dimensional spin-echo MR imaging of the brain” in Radiology, 2000; 216(3):891-899). However, these methods furthermore have the disadvantage that the later signal echoes receive a higher T2 weighting given long echo trains.
US 2004/0051527 A1 describes an acquisition method with long echo trains in which the magnetization is inverted before switching the multiple of refocusing pulses with variable flip angle. An associated increasing T2 weighting, however, can also not be prevented with this.